Electrical-apparatus casing



Alig- 1929. w. J. DICKENSON 1,725,623

ELECTRICAL APPARATUS CASING Filed July 23 1928 Inventor: Wil l'amJ.Dickenson, y (4/4 H is Attorney.

Patented Aug. 20, 1929.

UNITED STATES WILLIAM J. DICKENSON, OF PITTSFIELD,

MASSACHUSETTS, ASSIGNOR T0 GENERAL ELECTRIC COMIPANY, A CORPORATION OFNEW YORK.

ELECTRICAL-APPARATUS CASING.

Application filed July 23,

My invention relates to electrical apparatus casings, and moreparticularly to arrangements for relieving excessive pressures caused byexplosions within such casings. Casings containing an insulating liquidare often used for electrical apparatus such as transformers, theelectrical apparatus being immersed in the liquid for insulating andcooling purposes. The liquid is heated by the apparatus and willdeteriorate rapidly if the oxygen of the outside air reaches it. Thecasings are generally tightly closed, therefore, except for a smallopening to permit expansion and contraction caused by variations intemperature. If there is a defect in the insulation of the apparatus orif the apparatus is subjected to an excessive voltage, the insulationmay break down with a resulting arc in the insulating liquid. Such acondition may produce an extremely rapid increase in pressure within thecasing.

Pressure relief pipes are often used to relieve excessive internalpressure in electrical apparatus casings. These pipes are of largecross-section to permit rapid escape of gases from the casings and theyare normally closed at their outer ends by seals which yield to internalpressure. These pipes extend above the casings so that they contain gascushions in their upper ends to help absorb the initial shocks ofexplosions in the casings.

It is practically impossible to keep the insulating liquid absolutelyfree of moisture. \Vhen the liquid is heated, any moisture which itcontains may vaporize and ascend into the pressure relief pipe which iscooled by the surrounding air. If the vaporized moisture condenses onthe inner surface of the pipe or if any moisture enters the pipe througha leaky joint or past its end seal, such moisture tends to run down intotheorising where it may reach the electrical apparatus and result in aweakening and breakdown of the insulation. The general object of theinvention is to provide an electrical apparatus casing with a pressurerelief pipe having an improved arrangement and construction whereby anymoisture reaching the interior of the pipe cannot reach the interior ofthe casing and the apparatus therein.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing in which Fig. 1 showsa pressure relief pipe constructed in accordance with the invention,

1928. Serial No. 294,849.

the pipe being shown partly in section, and Fig. 2 shows the samepressure relief pipe mounted on a transformer casing.

Like reference characters indicate similar parts in both figures of thedrawing.

The invention will be explained in connection with the casing of an oilimmersed transformer. In the particular arrangement shown in thedrawing, the transformer 10 is immersed in a body of insulating oil 11within a casing 12. The casing 12 is tightly closed to exclude outsideair except for a small pipe 13 which connects the casing with anexpansion chamber 11 to permit expansion and contraction of the oil 11as its temperature varies.

The pressure relief pipe 15 communicates with the interior of the casing12, being mounted on the cover of the casing and extending upwardlytherefrom. The outside air is normally excluded from the pipe 15 by anend seal 16 which may be a glass diaphragm and which will yield orrupture in response to excessive pressure within the casing 1.2 and pipe15 to relieve such pressure and prevent rupture of the casing. The pipe15 is of large cross-section so that sudden large increases of pressurewithin the casing may be relieved quickly. The oil 11 may extend a shortdistance into the lower part of the pipe 15 but it has been founddesirable to extend the pipe well above the oil level so that the upperpart of the pipe may contain a cushion of air or other to help absorbthe initial shock of any explosion in the casing 12.

An extremely small proportion of moisture in the oil will so lower itsdielectric strength as to make it unfit for use but it is generallyimpossible to keep the oil absolutely free from all traces of moisture.\Vhen the oil is hot, there is a tendency for any traces whatever ofmoisture in the oil to be vaporized and rise to mix with the gas in theupper part of the pipe15. There is then a tendency for this moisture tocondense on the inner surface of the pipe because the surrounding airkeeps the pipe cooler than the gas cushion within it. If the condensedmoisture is permitted to run down into the casing, it may settle ontothe transformer and cause a failure of the insulation and possibly anexplosion.

The pressure relief pipe 15 includes a base section 17 mounted on thecasing 12 and an upper section 18 connected at its lower edge to theinterior of the pipe and closed at itslower endby the welded joint 19.

Any condensation of moisture will be on the inner surface of the upperor outer section 18 because the reduced inner part of the base section17is protected from the cooling effect of the surrounding air by the airspace 20. Condensed moisture collects in the space 20 whence it may bedrawn off at intervals by removing the drain plug 21. There is animportant advantage in forming the welded joint on the outer surface ofthe base section 1? because if this joint is not absolutely leak pro-ofany condensed moisture in the space 20 cannot leak into the pipe andfind its way into the casing 12 but will appear outside ofthe pipe whereit can do no harm.

The reduced upper part of the base section 17 is shown in the drawing asextending consiredably above the oil level where spacing blocks 22 areprovided between the two sec tions. This keeps the space 20 free of oilbut this is not of particular importance. If the upper end of the space20 is below the oil level so that the oil may enter this space, anycondensed moisture will still be collected because it is heavier thanthe oil and will settle through it.

The invention has been explained by describing and illustrating apreferred form thereof but it will be apparent that various changes maybe made without departing from the scope of the invention as defined inthe appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedSit-ates, is

1. A pressure relief pipe for electrical apparatus casings, said pipeincluding spaced inner and outer portions, the space between saidportions being open at its upper end to receive moisture condensed onthe inner surface of said outer portion.

2. A pressure relief pipe for electrical apparatus casings, said pipeincluding spaced inner and outer portions, the space between saidportions being open at its upper end to receive moisture condensed onthe inner surface of said outer portion, and the lower edge of saidouter portion being welded to the outer surface of said inner portion,whereby condensed moisture leaking through said weld cannot enter saidpipe.

3. A pressure relief pipe for electrical apparatus casings, said pipeincluding a base section and an upper section, said base sectionextending into said upper section and being spaced therefrom, the loweredge of said upper section being welded to the outer surface of saidbase section, and the space between said sections being open at itsupper end to receive moisture condensed on the inner surface of saidupper section.

4. A pressure relief pipe for electrical apparatus casings, said pipeincluding a base section and an upper section, said base section havinga reduced portion extending into said upper section and spacedtherefrom, the lower edge of said upper section being welded to theouter surface of said base section, and the space between said sectionsbeing open at its upper end to receive moisture condensed on the innersurface of said upper section.

In witness whereof, I have hereunto set my hand this 19th day of July,1928.

l/VILLIAM J. DICKENSON.

